The present invention relates to a transmission and a working vehicle.
A plurality of planetary gear mechanisms and a plurality of clutches, which are for switching between connection and disconnection of rotation elements in the planetary gear mechanisms, are provided in a transmission. For example, a transmission which is provided with a first planetary gear mechanism and a second planetary gear mechanism is disclosed in Japanese Unexamined Patent Application Publication No. 2006-329244. In this transmission, connection and disconnection of a carrier of the second planetary gear mechanism and a housing is switched using a low speed clutch. In addition, connection and disconnection of a carrier of the second planetary gear mechanism and a ring gear in the first planetary gear mechanism is switched using a high speed clutch.
At the same time, a return spring for returning the clutch to a state of disconnection is typically provided in the clutch. The return spring presses a piston in the clutch in a direction which returns the clutch to a state of disconnection. For example, the piston applies pressure to a clutch plate against the pressing force of the return spring due to hydraulic fluid being supplied to a hydraulic fluid chamber of the piston when the clutch is connected. The hydraulic fluid is discharged from the hydraulic fluid chamber of the piston by the piston being returned due to the pressing force of the return spring when the clutch is disconnected.